This invention relates to apparatus and methods for testing characteristics of animal bones, for example human bones, by transmitting ultrasonic energy through bone tissue to be tested.
The testing of bone tissue characteristics such as bone mineral density (BMD) in living humans is widely utilized in present-day medical practice to determine whether and to what extent a patient has osteoporosis or other bone disease. One convenient and effective way of testing bone tissue characteristics is by transmitting ultrasonic energy through a bone in a patient""s limb or extremity, between ultrasonic transducers respectively disposed on opposite sides of the limb or extremity, while the transducers and bone-containing limb or extremity are stably held in stationary, predetermined relation to each other in a support or frame. It is currently preferred, in at least many instances, to perform ultrasonic testing on the heel bone (os calcis, or calcaneal bone), with the foot of the patient positioned in the support and the ultrasonic transducers facing each other on opposite sides of the heel.
For effective coupling of ultrasonic energy to the heel, some testing systems (wet systems) include a tank or container of liquid in which the foot is immersed, and which is in contact with the transducers. Dry systems have also been developed, in which a pair of pads constituted of a suitable polymer or filled with a liquid coupling medium such as a gel (the term xe2x80x9cliquidxe2x80x9d herein embracing gels) are respectively disposed between the heel and the two transducers, each pad being in contact with and somewhat compressed between its associated transducer and the heel.
The transducers employed are devices for converting electrical energy to ultrasonic energy and vice versa. Thus, one of the transducers is energized electrically to generate ultrasonic energy which is transmitted through the heel or other body portion containing the bone being tested and received by the other of the transducers. The receiving transducer in turn generates an electrical signal in response to the received ultrasonic energy which has traversed the bone. This electrical signal is detected by appropriate electrical circuitry and utilized in deriving a value representing, for example, the speed of sound (SOS) through the bone or broadband ultrasonic attenuation (BUA) by the bone. Such values can be correlated with medically significant bone characteristics such as BMD.
In conventional systems as heretofore known, each of the ultrasonic transducers which produce and receive the ultrasonic energy is typically a ceramic piezoelectric crystal heavily damped with a composite backing and/or tuned to obtain the desired broadband frequency response. These transducers are extremely labor-intensive to manufacture, requiring an extensive amount of machining, gluing and compressing in production. Because of the many manufacturing steps, the nature of the ceramic crystal and the damping backing, the final product is extremely variable in nature. This variability is manifested in frequency response, amplitude and ultrasonic wave shape.
The present invention, in a first aspect, broadly contemplates the provision of ultrasonic bone testing apparatus comprising a pair of ultrasonic transducers at least one of which comprises a piezoelectric copolymer; mounting structure supporting the transducers in facing spaced relation to each other, so as to be respectively positionable on opposite sides of and both coupled ultrasonically to an animal portion containing a bone, for respectively transmitting ultrasonic energy through and receiving ultrasonic energy transmitted through the animal portion including the bone; and electrical circuitry connected to the transducers to energize one transducer to transmit ultrasonic energy and to detect an electrical signal generated by the other transducer in response to received ultrasonic energy.
In this apparatus, the mounting structure may include a support for positioning the animal portion between the transducers, and a device for coupling the transducers ultrasonically to the animal portion. Preferably, both transducers are piezoelectric copolymer transducers. Each of the transducers typically or conveniently comprises a plate of a piezoelectric copolymer, the term xe2x80x9cplatexe2x80x9d being used herein to denote a generally flat element such as a sheet, slab or film, whether self-sustaining or coated on a substrate layer and/or itself provided with a protective or other coating. Alternatively, since the copolymer of the transducer is easily shaped, either or both of the copolymer transducers included in the present invention may have a curved surface, to provide focusing, and/or may be constituted as an array of multiple discrete copolymer transducer elements, such an array having advantages for correction for phase cancellation and/or for imaging; in such an array, the individual elements of the array could correspond to pixels and each pixel could have a different BUA, SOS or BMD value.
A currently preferred embodiment of the invention includes two copolymer transducers, respectively serving as a transmitter and a receiver of ultrasonic energy, and each comprising a copolymer disk having a periphery and two opposed major surfaces, one of which is disposed to face the bone-containing animal portion. In accordance with a particular feature of the invention, in this embodiment each such transducer further includes a rigid support structure, such as (for instance) a rigid ring, engaging the other major surface of the disk inwardly of the periphery thereof for supporting the disk against pressure exerted on the first-mentioned major surface of the disk. For example, in embodiments wherein the coupling device comprises a pair of polymer pads, each disposed in contact with one major surface of one of the transducers, and respectively engageable with opposed surface regions of an animal portion positioned in the support as aforesaid, the rigid support structure (e.g., ring) engaging the other major surface of each transducer disk inwardly of the periphery thereof supports the disk against pressure exerted on the disk through the last-mentioned pad.
In other embodiments, the coupling device includes a container for holding a body of a coupling fluid in which the animal portion is immersed when positioned by the support as aforesaid and with which the transducers are in ultrasonic energy transmitting contact.
Any of these embodiments may be arranged for use in testing procedures in which the animal portion is a human heel, the support being configured and dimensioned to position the heel, and the transducers and coupling device being disposed, SQ that ultrasonic energy transmitted from one transducer to the other transducer passes through the calcaneal bone of the heel.
The electrical circuitry may be arranged to use the detected electrical signal in deriving a value representative of the speed of sound through the bone through which the ultrasonic energy is transmitted as aforesaid. Alternatively, or additionally, the circuitry may be arranged to use the detected electrical signal in deriving a value representative of broadband ultrasonic attenuation (BUA) in the bone.
In a second aspect, the invention contemplates the provision of a method of determining a characteristic of a bone in a bone-containing portion of an animal comprising disposing a pair of ultrasonic transducers at least one of which comprises a piezoelectric copolymer respectively on opposite sides of, and ultrasonically coupling both transducers to, a bone-containing animal portion; electrically energizing one transducer to transmit ultrasonic energy through the animal portion including the bone, such that the transmitted ultrasonic energy is received and converted to an electrical signal by the other transducer; detecting the electrical signal; and using the detected signal to derive a value representative of the bone characteristic to be determined. Again, in embodiments wherein the transducers so used are disks of a piezoelectric copolymer, each having a periphery and opposed major surfaces, one of which is oriented to face the animal portion, the method of the invention further includes the feature of supporting the other major surface of each disk by disposing, in contact therewith, rigid support structure spaced inwardly from the disk periphery.
In the apparatus and method of the invention, the use of piezoelectric copolymer disks as transducers affords significant economies, as well as effective performance. The piezoelectric copolymer material requires fewer manufacturing steps and is less variable in ultrasonic properties than conventional ceramic piezoelectric transducers; hence the use of this material enables a more uniform product to be manufactured. The provision of the rigid support structure, spaced inwardly of the periphery of the copolymer disk, enables such use of these relatively deformable and/or frangible thin disks without distortion or breakage.
Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawings.